1. Field of the Invention
The present invention relates to a Broadband Wireless Access (BWA) communication system, and more particularly to a method and a system for forming and transmitting/receiving neighbor Base Station (BS) information in order for a serving BS to send the neighbor BS information to a Mobile Station (MS) in a BWA communication system.
2. Description of the Related Art
The communication system was initially developed for the purpose of voice service and is now being developed to provide data service and various multimedia services. However, the communication system developed for voice service has a relatively narrow bandwidth for data transmission and requires relatively expensive service charges, it cannot meet rapidly increasing user demands for various services. Further, the necessity for a communication system capable of efficiently providing Internet service is now increasing due to increasing demands for the Internet service together with the development in the communication industry. To this end, a Broadband Wireless Access (BWA) communication system, which has a broad enough bandwidth to meet rapidly increasing user demands and efficiently provide the Internet service, has been introduced.
The BWA communication system is a communication system for supporting not only the voice service but also various data services of low and high speed and multimedia application services for providing high quality moving images, etc. The BWA communication system supports access to the Public Switched Telephone Network (PSTN), Packet Switched Data Network (PSDN), Internet network, International Mobile Telecommunication (IMT)-2000 network, Asynchronous Transfer Mode (ATM) network, etc. in a mobile or stationary environment based on wireless media using a broadband, and supports a high speed channel data rate. The BWA communication system can be classified into a broadband wireless subscriber network, a broadband mobile access network, and high speed wireless Local Area Network (LAN), according to the mobility (stationary or mobile) of a Subscriber Station (SS), the communication environment (outdoor or indoor), and the channel data rate.
Meanwhile, 802.16 standardization group of Institute of Electrical and Electronics Engineers (IEEE), which is one of international standardization organizations, is arranging standards for wireless access schemes of the BWA communication system, and specifically, is now driving to establish an IEEE 802.16d standard for providing a broadband wireless Internet service to a stationary SS. The 802.16 system does not account for the mobility of the SS.
A BWA system according to the IEEE 802.16d standard has a wider bandwidth for data transmission and thus can transmit a much larger quantity of data in a short time, in comparison with the conventional wireless technology for voice service. Further, in the BWA system according to the IEEE 802.16d standard, all of the users can share a channel, thereby achieving efficient use of the channel. Further, the BWA system according to the IEEE 802.16d standard can guarantee various Quality of Service (QoS) and thus can provide a user with services of different qualities according to the characteristics of service. In the IEEE 802.16d system, all of the users connected to the BS share a common channel, so the BS allocates intervals of the common channel for use by each user during every uplink and downlink frame. Therefore, the BS must send uplink and downlink access information to the users every frame in order to enable the users to share the channel. To this end, in the IEEE 802.16d system, channels are divided into uplink channel and downlink channel, information about each channel is defined according to Type, Length and Value (TLV), and the defined information is then inserted to Downlink Channel Descriptor (DCD) and Uplink Channel Descriptor (UCD) messages which are transmitted to all of the users, so that characteristic information about the channels is sent to the SS.
Further, the IEEE 802.16 standardization group is now driving to establish an IEEE 802.16e standard for providing mobility to an SS of the IEEE 802.16d communication system. The IEEE 802.16e communication system has a wider bandwidth for data transmission and thus can transmit a much larger quantity of data in short time, in comparison with the conventional wireless technology for voice service. Further, in the IEEE 802.16e communication system, all of the users can share a channel, thereby achieving efficient use of the channel. Also, the IEEE 802.16e communication system can guarantee various Quality of Service (QoS) and thus can provide a user with services of difference qualities according to the characteristics of service. The IEEE 802.16e communication system supports handoff, thereby guaranteeing the mobility of a Mobile Station (MS).
In order to support the mobility of an MS, a BS of the IEEE 802.16e communication system periodically broadcasts a mobile neighbor advertisement (MOB_NBR-ADV) message that includes neighbor BS information to all MSs within a cell controlled by the BS, thereby sending status information of the neighbor cells to the MSs. Specifically, when an MS located within one cell moves to a neighbor cell, the MS can preliminarily obtain information of a neighbor BS of the neighbor cell (i.e. a BS controlling the neighbor cell), such as a network ID, channel characteristics, etc. of the neighbor BS, by receiving the MOB_NBR-ADV message broadcast by the serving BS which controls the current cell in which the MS is currently located. Therefore, the IEEE 802.16e communication system can support handoff of the MS.
However, in the IEEE 802.16e communication system, when the serving BS has too many neighbor cells or the neighbor cells have capacities much different from the capacity of the current cell, the quantity of the neighbor BS information transmitted from the serving BS to the MSs becomes too much, so that the MOB_NBR-ADV message transmitted from the serving BS to the MSs becomes too large. When the serving BS has too much neighbor BS information, it is impossible to transmit all of the information in one frame. In other words, the MOB_NBR-ADV message including all the neighbor BS information becomes too large and thus cannot be transmitted in one frame. In the IEEE 802.16e communication system, a BS cannot fragment a Medium Access Control (MAC) management message to transmit the message.